Lighting apparatus having low profile

ABSTRACT

Disclosed is a low profile lighting apparatus that is particularly advantageous for use as a backlight for illuminating a display. The lighting apparatus includes a waveguide coupled to a light source for injecting light into the waveguide. The waveguide includes a plurality of elongate structures for ejecting light propagating within the waveguide through a predetermined surface of the waveguide. Another embodiment of the waveguide includes a central region of reduced thickness that redirects light propagating within the waveguide. The lighting apparatus has a low profile so it is particularly useful in areas of limited space.

This application is a continuation-in-part of U.S. patent applicationSer. No. 08/764,298, filed Dec. 12, 1996, entitled “Waveguide with LightEmitting Diodes for Illumination and Display.”

BACKGROUND OF THE INVENTION

The present invention relates to a lighting apparatus. Moreparticularly, the present invention relates to a low profile lightingapparatus utilizing a waveguide for illumination. The invention isparticularly advantageous for use as a backlight for illuminating adisplay.

Backlights may be used to illuminate both mechanical displays, such ason analog watches or automobile gauges, as well as electronic displays,such as liquid crystal displays used with cellular phones, and pagers,and personal digital assistants. Because many backlight applicationsinvolve smaller displays where space is at a premium, it is desirable toreduce the thickness of such backlights while still maintaining the areaof illumination. Backlights thus require reduced aspect ratios, definedas the ratio of the thickness of the backlight to the length of theillumination area.

One type of a backlight utilizes of a light source, such as alight-emitting diode (LED), that is coupled to a waveguide into whichlight is injected. The light source is typically mounted at an outerperipheral edge of the waveguide and is energized to emit light into thewaveguide. The light undergoes several reflections between the surfacesof the waveguide until being transmitted through a top surface toilluminate the display.

One difficulty associated with such backlights is they do not produce auniform intensity across the surface of the waveguide. The light losesintensity as it propagates outward from the light source. Consequently,as the distance from the light source increases, the intensity of thelight transmitted out of the waveguide decreases. This results in theportions of the waveguide distal of the light source having reducedintensity.

There is therefore a need for an efficient backlight having a low aspectratio that provides a substantially uniform illumination profile acrossthe entire area of illumination.

SUMMARY OF THE INVENTION

One aspect of the present invention relates to a lighting apparatus forilluminating an illumination area of a display. The lighting apparatuscomprises a waveguide adapted for mounting adjacent the display so as toilluminate the illumination area of the display. The waveguide comprisesa top surface having an optical output area corresponding in size to theillumination area, a bottom surface spaced apart from the top surface,and a side surface extending between the top and bottom surfaces.Reflective material is positioned adjacent the bottom and side surfacesof the waveguide. At least one light source is mounted to input lightproximate to a periphery of the waveguide between the top and bottomsurfaces. The waveguide further comprises a light ejector on one of thetop and bottom surfaces configured to redirect light propagating betweenthe surfaces towards the top surface for transmission therethrough. Thelight ejector is arranged to provide a preselected illumination profileacross the optical output area of the top surface.

Another aspect of the invention relates to a lighting apparatuscomprising a waveguide having pair of opposed surfaces. Each of thesurfaces is at least partially reflective and at least one of thesurfaces is partially transmissive. Each of the surfaces have areflectivity greater than the transmissivity of the at least onesurface.

Another aspect of the invention relates to a lighting apparatuscomprising a planar waveguide having a peripheral edge and a lightsource mounted proximate to the peripheral edge so as to direct lightinto the waveguide along a path extending from the light source towardsan optical diverter in the waveguide. The optical diverter in the pathredirects light rays away from the path towards the periphery of thewaveguide.

Yet another aspect of the invention relates to a lighting apparatuscomprising a top surface, a bottom surface in spaced relationship to thetop surface and cooperating with the top surface to form a waveguidehaving a thickness defined by the distance between the top and bottomsurfaces, and at least one solid state point light source mounted toinput light into the waveguide between the surfaces. One of the surfaceshas a curvature relative to the other surface which yields a substantialvariation in the thickness of the waveguide in a selected region of thewaveguide. The variation follows a geometric contour selected toredirect light propagating between the surfaces of the waveguide so thatthe redirected light exits the top surface of the waveguide.

Another aspect of the invention relates to a lighting apparatuscomprising a waveguide having top and bottom surfaces and a peripheraledge. The waveguide has a thickness defined by the distance between thetop and bottom surfaces. The thickness at the peripheral edge issubstantially different than the thickness in a region intermediateopposing sides of the peripheral edge. The thickness has a geometryselected to enhance ejection of light from the top surface intermediatethe opposing sides. At least one light source is disposed proximate tothe peripheral edge to introduce light into the waveguide between thetop and bottom surfaces.

Yet another aspect of the invention relates to a lighting apparatuscomprising a waveguide of solid material, the waveguide having a topsurface, a bottom surface and a side surface. A light source is mountedto input light into the waveguide and reflective material is juxtaposedwith one of the top and bottom surfaces wherein at least a portion ofone of the top and bottom surfaces has a pattern of elongate structuresthat generally increase in density with distance from the light source.

In yet another aspect of the invention, there is disclosed anillumination and display device comprising an optical waveguiding layerand an illumination coupler embedded in an interior region of thewaveguiding layer. In one embodiment, the illumination coupler includesone or more semiconductor light emitting devices. A portion of theoptical waveguiding layer has a pair of symmetric (a) nonplanar, curvedsurfaces, or (b) a plurality of flat, planar surfaces approximating thenonplanar, curved surface. The pair of symmetric surfaces form a cusplying on the axis of the one or more semiconductor light emittingdevices to produce total internal reflection of light from the one ormore semiconductor light emitting devices into the waveguiding layer.Display elements are formed on surfaces of the waveguiding layer tocause light to be emitted from the waveguiding layer.

Another aspect of the invention relates to an illumination and displaydevice, comprising an optical waveguiding layer, with an illuminationcoupler embedded in an interior region of the waveguiding layer, whereinthe illumination coupler includes one or more semiconductor lightemitting devices. Display elements formed on the surface of thewaveguiding layer cause light to be emitted from the waveguiding layer.

Yet another aspect relates to an illumination and display device,comprising an optical waveguiding layer with an illumination couplerembedded in an interior region of the waveguiding layer. In oneembodiment, the illumination coupler includes one or more semiconductorlight emitting devices, each of the one or more semiconductor lightemitting devices having a longitudinal axis that is parallel to thesurface of the optical waveguiding layer. A hole or recess may be formedin the interior region of the waveguiding layer where the one or moresemiconductor light emitting devices is placed. The device also maycomprise display elements formed on the surface of the waveguiding layerto cause light to be emitted from the waveguiding layer.

A further aspect of the invention is directed to an illumination devicecomprising a waveguide having an illumination coupler embedded in aninterior region thereof. The waveguide has generally parallel top andbottom surfaces outside of the interior region such that light is guidedtherebetween. The illumination coupler comprises a refractive indexinterface configured to capture light rays propagating along a line thatforms less than the critical angle of total internal reflection withrespect to at least one of the top and bottom surfaces, such that thecaptured light rays are injected therebetween for propagation outside ofthe interior region. In one embodiment, the illumination couplercomprises a surface configured for total internal reflection of lightincident thereon. The illumination coupler of this embodiment isintegrally formed with the waveguide from a single piece of transparentmaterial, and the reflecting surface is uncoated. A point source oflight is disposed at least partially, preferably fully, within a cavityformed in the waveguide adjacent the total internal reflecting surface.Display elements may be included on at least one of the surfaces forejecting light from the waveguide. Additionally, diffusive reflectivematerial may be included on at least one of the top and bottom surfaces.

In yet another aspect of the invention, there is disclosed a lightingapparatus, comprising a device that emits light and an optical cavitythat is formed by diffusive reflective surfaces, the cavity having anoutput region through which light from the cavity passes. The lightemitting device is mounted to supply light to the cavity while beinghidden from direct view through the output region. The cavity has adiffusely reflective surface area and the output region also has anarea. The ratio of the area of the output region to the sum of (i) thearea of the output region and (ii) the surface area of the cavity is atleast 0.05. Additionally, the cavity has a depth and the output regionhas an edge to edge bisector dimension, the ratio of the depth to thebisector dimension being significantly less than 0.1. The lightingapparatus additionally comprises an angular spectrum restrictorpositioned to restrict output illumination through the output region toa predetermined range of angles.

Another aspect of the invention involves a method of lighting. Themethod comprises producing illumination from an optical cavity formed bydiffusely reflecting surfaces and outputting illumination from thecavity through an output illumination region. Producing of theillumination comprises directing light rays from a source ofillumination into the cavity such that the source of the illumination isnot visible through the output illumination region. The method furthercomprises restricting the angular spectrum of illumination from theoutput illumination region to a predetermined range of angles, andmounting the optical cavity to illuminate at least a portion of a room.

In another aspect of the invention, there is disclosed a method ofmanufacturing a lighting apparatus. One embodiment of the methodcomprises wrapping a flexible sheet of reflective material around oneside of a tubular light source, juxtaposing a member forming an opticalcavity with another side of the tubular light source so that light fromthe source is introduced into the optical cavity, and attaching theflexible sheet to the member such that the sheet retains the tubularsource in juxtaposition with the member.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the invention will now be described withreference to the drawings of a preferred embodiment, which are intendedto illustrate and not to limit the invention, and in which:

FIG. 1 is a perspective view of wristwatch incorporating one embodimentof a lighting apparatus;

FIG. 1A is a cross-sectional view of the watch of FIG. 1 taken alongline 1A—1A;

FIG. 2 is a top plan view of the lighting apparatus used to illuminatethe watch of FIG. 1;

FIG. 3 is a cross-sectional side view of the lighting apparatus of FIG.2 taken along the line 3—3;

FIG. 4 is a cross-sectional view of the lighting apparatus of FIG. 2taken along the line 4—4;

FIG. 4A is an enlarged view of a portion of FIG. 4;

FIG. 4B is a cross-sectional view similar to that of FIG. 4, but withelongate structures on the top surface;

FIG. 4C is a cross-sectional view similar to that of FIG. 4, but withreflective material surrounding the entire waveguide;

FIG. 5 is a top plan view of an alternative embodiment of a waveguidefor use in the lighting apparatus of FIG. 2;

FIG. 6 is a top plan view of yet another embodiment of a waveguide foruse in the lighting apparatus of FIG. 2;

FIG. 7 is a top plan view of yet another embodiment of a waveguide foruse in a lighting apparatus;

FIG. 8 is a top plan view of a waveguide showing another embodiment ofan optical diverter;

FIG. 9 is a cross-sectional view of a lighting apparatus used with alight enhancing structure;

FIG. 10 is a top plan view of a waveguide having a dimple forredirecting light rays;

FIG. 11 is a cross-sectional side view of the lighting apparatus of FIG.10 taken along the line 11—11;

FIG. 12 is a perspective view of an alternate embodiment of a lightingapparatus;

FIG. 13 is a cross-sectional view of the lighting apparatus of FIG. 12;

FIG. 14 is a perspective view of a housing used with the lightingapparatus of FIG. 12;

FIG. 15 is a perspective view of a lighting apparatus including a totalinternal reflection region;

FIG. 16 is cross-section view of the lighting apparatus of FIG. 15 takenalong the line 16—16;

FIG. 16A is an enlarged view of a portion of FIG. 16;

FIG. 17 is a perspective view of an alternative embodiment of a lightingapparatus including a total internal reflection region;

FIG. 18 is a cross-sectional view of the lighting apparatus of FIG. 17taken along the line 18—18;

FIG. 19 is a schematic side view of a prior art “bullet lens” LED;

FIG. 20 is a schematic side view of a prior art “bare” LED;

FIG. 21 is a perspective view of an exit sign incorporating analternative embodiment of a lighting apparatus;

FIG. 22 is a rear perspective view of an automobile having taillightsthat incorporate a lighting apparatus;

FIG. 23 is a top view of a wrist watch incorporating an alternativeembodiment of a lighting apparatus;

FIG. 24 is a cross-sectional side view of the exit sign of FIG. 21 takenalong the line 24—24;

FIG. 25 is a perspective view of an exit sign incorporating yet anotherembodiment of a lighting apparatus;

FIG. 26 is a side view of an exit sign incorporating extractive displayelements;

FIG. 27 is a side view of an extractive display element;

FIG. 28 is a side view of an alternative embodiment of an extractivedisplay element;

FIG. 29 is a perspective view of an exit sign incorporating circulargrooves for extracting light; and

FIG. 30 is a cross-sectional side view of the exit sign of FIG. 29.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIGS. 1 and 1A, one embodiment of the present invention isutilized as a back lighting apparatus 26 for a wristwatch 20. Althoughthe wristwatch 20 is shown having a generally circular shape, it will beappreciated that the wristwatch may have any of a variety of shapes.

An outer housing 22 of the wristwatch 20 encloses a thin disk 30 ofsubstantially transparent material that is spaced below a watch crystal24. The disk 30 has an upper display surface 32 and an opposed bottomsurface 34. The display surface 32 includes indicia 35 (FIG. 1), such asnumerals for indicating time, although other indicia could also bedisplayed. Two hands 36 of the watch 20 are mounted for rotation about astem 38 that extends through the disk 30. The stem is driven by a watchmechanism 40 in a well known manner. Alternatively, the disk 30 maycomprise a liquid crystal display in which indicia, such as the handsand numerals, are electrically generated.

Referring to FIG. 1A, the lighting apparatus 26 is interposed betweenthe disk 30 and watch mechanism 40 for illuminating the disk 30. Thelighting apparatus 26, which is preferably in contact with the disk 30,includes a waveguide 42 and a light source 44 positioned along aperipheral edge of the waveguide 42.

In the illustrated embodiment, the housing 22 supports the disk 30 andthe lighting apparatus 26 in juxtaposed relationship to each other. Thedisk 30 is mounted so that its periphery is supported by a first annularlip 46 which partially covers the display surface 32 to define a viewingarea or illumination region of the display surface 32. The waveguide 42,which has a diameter slightly larger than that of the disk 30, ismounted so that its periphery is supported by a second annular lip 48 inthe housing 22. The second annular lip 48 is sized to shield the lightsource 44 from being directly visible through the illumination region ofthe display surface 32. By way of example, the diameter of theillumination region may be 27 mm.

As shown in FIG. 2, the waveguide 42 has a circular shape optimal forilluminating a circular watch, although other shapes may be utilized forvarious applications. The light source 44 is mounted within a triangularor V-shaped notch 50 in the peripheral edge of the waveguide 42. Thenotch 50 serves as an optical diverter which redirects light transmittedby the light source 44, utilizing refractive index differences at theinterface 52 formed by the sides of the notch 50. In a preferredembodiment, the V-shaped optical diverter 50 is symmetrical such that aline passing through its apex and the center of the waveguide 42 bisectsthe V-shaped notch.

In a preferred embodiment, the light source is a single, solid state,point source of light, such as a light emitting diode (LED) 44 mountedon a carrier or circuit board (not shown). The carrier on which the LED44 is mounted is attached to the waveguide at the back of the notch 50(i.e., the open end opposite the apex) utilizing an adhesive (notshown). The LED 44, which is typically in the form of a cube of solidstate material that emits light from each of multiple faces (i.e., itstop surface and four sides), is spaced from the sides of the notch 50with air therebetween. The difference in index of refraction between thewaveguide and the air creates the refractive index interface 52 thatcauses light to refract as the light passes into the waveguide 42. Inaccordance with this advantageous feature, a substantial fraction of thelight passing through the interface 52 is refracted toward oppositesides of the waveguide 42 (i.e., the sides generally adjacent to and onopposite sides of the light source 44). In this manner, regions of thewaveguide 42 that are located to the sides of the light source 44 areefficiently illuminated, and the diverter 50 thereby contributes touniform illumination.

The waveguide 42 is preferably comprised of a material that istransparent to light produced by the LED 44, such as a transparentpolymeric material, and may be manufactured by various well-knownmethods, such as machining or injection molding. Preferred materials forthe waveguide 42 are acrylic, polycarbonate, and silicone. Acrylic,which has an index of refraction of approximately 1.5, is scratchresistant and has a lower cost relative to polycarbonate. Polycarbonate,which has an index of refraction of approximately 1.59, has highertemperature capabilities than acrylic. Polycarbonate also has improvedmechanical capabilities over acrylic. Silicone has a refractive index ofapproximately 1.43. The refractive index of air is 1.0. The dimensionsof the waveguide 42 may vary, although the waveguide 42 is desirablyvery thin relative to its length so as to provide a low profile. Thedistance between the top surface 56 and the bottom surface 58 ispreferably on the order of 1-3 mm, while the diameter of the waveguide42 is typically at least 2.0 mm.

As shown in FIG. 2, a plurality of display elements comprising elongatestructures 54 extend across the waveguide 42 for redirecting lightpropagating within the waveguide 42. Although illustrated as lines, theelongate structures 54 have a three-dimensional shape, as described indetail below. In the illustrated embodiment, the elongated elongatestructures 54 are arranged in a pattern consisting of intersecting linesthat extend radially outward from a common point at the center of thewaveguide 42 through which the stem 38 passes. The elongate structures54 are preferably spaced apart by an equal angular distance, such as 0.3degrees. It has been found that the pattern of radial grooves utilizedin the watch 20 are highly effective in eliminating “shadows” that wouldotherwise be cast by the watch stem 38.

As illustrated in FIG. 3 the waveguide 42 includes a top surface 56 andan opposed bottom surface 58, which are substantially parallel to eachother. A side or edge surface 60 extends between the top and bottomsurfaces 56, 58 along the periphery of the waveguide 42. While thesurfaces 56, 58 are typically flat for backlight applications, thesurfaces 56, 58 may also be formed as curved surfaces, such as when thewaveguide is utilized as a taillight for an automobile.

A diffusive reflective material 62 is positioned adjacent the bottomsurface 58 and side surface 60 of the waveguide 42, with the material 62also preferably covering a peripheral strip 61 on the top surface 56. Inthe embodiment illustrated, the peripheral strip 61 is sufficiently wideto cover the notch 50 so that the top, the bottom, and the outside edgeof the notch 50 are covered by the reflective material 62. Theperipheral strip is also preferably sufficiently wide that the LED 44cannot be viewed directly from viewing angles of 75 degrees or less (itbeing understood that the viewing angle is measured from a line normalto the top surface 56). By way of example, the peripheral strip may beequal in width to the width of the second annular lip 48 of the watch 20(FIG. 1).

The diffusive reflective material 62, which has a reflectivity of atleast 88% may comprise a single layer or multiple layers of diffuselyreflective tape, such as DRP™ Backlight Reflector, manufactured by W. L.Gore & Associates. DRP™ Backlight Reflector has a reflectivity ofapproximately 97%-99.5%, depending on its thickness and the wavelengthof the light. Alternatively, the reflective material 62 could comprise apaint or coating that is applied to the surfaces 58 and 60, such aswhite house paint or a more exotic material, such as the LabsphereCorporation's Spectraflect paint. Spectraflect paint's reflectivity isconsiderably higher than house paint, roughly 98%, while thereflectivity of a good white house paint is approximately 90%.

Because the reflective material 62 covers the bottom and side surfaces58, 60, as well as the peripheral strip on the top surface 56, lightwill be emitted from the waveguide in an output illumination region oraperture 65 comprising the central uncovered portion of the top surface56 (i.e., the portion of the surface 56 interior to the peripheral strip61). It will be appreciated that light rays incident on the top surface56 at an angle of incidence (i.e., the angle of the ray relative to aline normal to the surface) at least equal to a critical angle will betotally internally reflected toward the bottom surface 58. That is, thetop surface 56 will reflect all of such light back into the waveguide42. Light rays having an angle of incidence less than the critical angleare transmitted through the top surface 56. The value of the criticalangle is dependent on the difference in the indices of refractionbetween the waveguide 42 and the disk 22, as is known by those skilledin the art. For a waveguide 42 having a refractive index of 1.5, thecritical angle is approximately 42° when surrounded by air.

As shown in FIGS. 4 and 4A, the elongate structures 54 may comprisegrooves defined by surfaces 64 (FIG. 4A) that form a substantiallytriangular or V-shaped cross-section. The elongate structures 54advantageously alter the angle of incidence of light reflected towardthe top surface 56 to enhance passage therethrough. That is, the angledsurfaces 64 reflect light toward the top surface 56 at an angle ofincidence less than the critical angle so that such light passes throughthe top surface 56 rather than being totally internally reflected. Theelongate structures 54 are thus used to “eject” light rays that mightotherwise be totally internally reflected by the top surface 56. Thisadvantageously increases the optical efficiency of the waveguide 42 byejecting light that would otherwise experience energy loss throughrepeated reflections. The elongate structures are defined by a depth Dand an apex angle θ that bisects the V-shaped structure 54. In thepreferred embodiment, depth D is in the range of 1-2 micrometers and theangle θ is approximately equal to 45 degrees. Preferably, an air gap ismaintained within the V-shaped structure 54 (i.e., the grooves are notfilled with reflective material).

The elongate structures 54 are preferably arranged to achieve generallyuniform illumination profiles across the illumination output region ofthe waveguide. In preferred embodiments, the uniformity ratio of theoutput illumination region, which is defined as the ratio of the highestintensity to lowest illumination within such region is no more than 2 to1.

Referring to FIG. 4B, in another preferred embodiment, the elongatestructures 54 are placed on the top surface 56 instead of the bottomsurface 58. The remaining aspects of this embodiment are identical tothose of the embodiment shown in FIG. 4.

In an additional embodiment, shown in FIG. 4C, the entire waveguide,including the top surface 56, bottom surface 58, and side surfaces 60are covered by reflective material 63, which is preferably the samediffusely reflecting type as the material 62, but is partiallytransmissive and partially reflective. Additionally, the material 63 hasa reflectivity that is greater than its transmissivity, that is, thereflectivity is greater than 50% and the transmissivity is less than50%. In one preferred embodiment, which may be utilized in the watch 20,the reflectivity is about 96% and the transmissivity is about 4%. Thisembodiment provides an output illumination which is substantiallyuniform, even without the elongate structures 54, although suchstructures may still be desirable to reduce shadows from the watch stem38 (FIG. 1A). This embodiment is also advantageous in that the indica(numerals, etc.) may be applied directly to the reflective material 63,thereby eliminating the need for the display disk 30.

Various types of groove patterns may be utilized as to improve theuniformity of the illumination within the region to be illuminated,depending on the situation. Referring to FIG. 5, the elongate structures54 may be arranged in a pattern of nonintersecting arcuate lines thatare arranged about the light source 44. In a preferred embodiment, theradius of curvature of the arcuate lines increases with distance fromthe point source 44. Additionally, the centers of the radius ofcurvature lie along a line passing through the point source and thecenter of the illumination region of the waveguide, with all suchcenters lying along such line (on the side of the waveguide that isfurther from the waveguide center than from the source 44). The arcuatelines are nonuniformly spaced apart to compensate for loss of intensityas the light propagates outwardly from the light source 44.Specifically, the spacing between the elongate structures 54 decreasesas the distance from the light source 44 increases so that the densityof the elongate structures 54 increases moving away from the lightsource 44. The increased density of elongate structures 54 desirablyincreases the ejection of light rays in these areas to compensate forthe distance from the source 44.

As shown in FIG. 6, the elongate structures 54 could also be arranged ina more complex pattern comprised of a combination of simpler patterns.For example, the patterns could take the form of arcuate lines thatemanate outward from the light source 44 and straight lines that extendradially outward from the center of the waveguide 42.

FIG. 7 shows a rectangular-shaped waveguide 42. Such a waveguide ispreferably used to illuminate a rectangular-shaped display, such as oncellular phones or personal digital assistants. Although reflectivematerial is not shown, it will be understood that this embodiment may beconstructed in the manner previously described. In the illustratedembodiment, multiple point light sources 44 are coupled to introducelight at spaced peripheral locations along the edge of the waveguide 42.Because multiple sources are employed, optical diverters such as thenotch 50 are optional, and may or may not be included. The elongatestructures 54 of this embodiment are arranged in concentric arcs aroundeach of the light sources 44 although various other patterns arecontemplated, including those discussed above.

FIG. 8 illustrates an alternative embodiment in which elongatestructures 54 are formed in a waveguide 42 a by scratching a top orbottom surface of the waveguide with an abrasive, such as sandpaper. Theabrading is preferably non uniform such that the density of thescratches or grooves increase with distance from the light source 44. Byway of specific example, in the rectangular waveguide shown in FIG. 8,the grooves are directed along the length of the rectangle, rather thanthe width. The groove pattern is generally amorphous on a local basis,but is substantially directional and nonrandom on a global basis.

FIG. 8 also illustrates an alternative embodiment of an optical diverterthat is formed by a triangular opening 50 a that extends through awaveguide 42 a at its periphery. The opening is between the light source44 and the output illumination region of the waveguide 42, and a linedrawn between the source and the center of such region bisects thetriangle while passing through its apex. As shown, the triangularopening 50 a has two sides which intersect at a location proximate tothe light source to form such apex.

The triangular opening 50 a is filled with a material, such as air,which has a refractive index significantly different from that of thematerial of the waveguide 42. The shape of the optical diverter 50 a andthe refractive index difference cause light emanating from the lightsource 44 to intersect the optical diverter 50 a at an angle ofincidence which results in total internal reflection of the lighttowards opposite sides of the waveguide 42. Thus, the optical diverter50 a, like the notch 50, redirects the path of light rays to regions ofthe waveguide that are on opposite sides of the light source 44.

Referring to FIG. 9, the top surface 56 of the wave guide 42 (oralternative embodiments thereof) may be covered with an angular spectrumrestrictor 72 that restricts the output radiation pattern from theoutput illumination region 65 of the waveguide to a predetermined rangeof angles (in this context, the term “spectrum” is used in the sense ofan angular spectrum rather than a wavelength spectrum). The angularspectrum restrictor 72 comprises a planar micro-replicated opticalstructure, such as a holographic diffuser, binary diffractive diffuser,or array of microlenses. In the preferred embodiment, the angularspectrum restrictor 72 comprises a brightness enhancing film (BEF)which, in addition to restricting the output spectrum, enhances theintensity of the illumination in the output illumination region 65. TheBEF 72 is preferably placed in physical contact with a diffuser 70 tocollectively form a light quality enhancing apparatus 73. Preferably,the diffuser 70 is disposed between the BEF 72 and the waveguide 42 andin contact with the waveguide 42. The purpose of the diffuser is toremove the effect of residual nonuniformities, such as cosmeticimperfections, in the surfaces of the waveguide 42. The diffuser 70 iscomprised of translucent material, typically a thin plastic surface orvolume diffuser, both of which are characterized by very low absorptionand minimum energy losses.

As mentioned above, the BEF 72 restricts output illumination withindefined boundary lines and also increases the brightness within theoutput illumination region 65. In the preferred embodiment, the BEF 72is a commercially available thin film having linear pyramidalstructures, such as 3M model 90/50 film. The BEF transmits only thoselight rays from the waveguide that satisfy certain incidence anglecriteria with respect to the top surface 56. All other light rays arereflected back into the waveguide 42 toward the bottom or side surfaces58 and 60, respectively, where they are reflected by the reflectivematerial 62. In effect, the reflected rays are “recycled” until they areincident on the BEF 72 at an angle which permits them to pass throughthe BEF 72.

As is well known, a BEF, such as the BEF 72, concentrates illuminationwithin boundaries defined by a pair of mutually inclined planes (whichin cross-section form a “V”) and does not provide concentration in theorthogonal direction. In some applications of the invention, it ispreferable to concentrate the illumination two orthogonal directions,and for such applications, a second BEF oriented orthogonally to thefirst BEF, may be included. With two crossed BEFs, the emission from thewaveguide will be within boundaries resembling a truncated invertedcone. As is conventional in the art, the boundaries are defined by thefull-width, half-maximum (FWHM) of the optical intensity. By way ofexample, the boundaries of the cone may be inclined relative to a linenormal to the top surface 56 by an angle of no more than about 35degrees, in which case the illumination will be visible only withinviewing angles of 35 degrees or less.

FIGS. 10 and 11 illustrate a top and a cross-sectional side view,respectively, of yet another embodiment of the lighting apparatus 26that utilizes a waveguide 42 b. As shown in FIG. 10, a light source 44is mounted adjacent an optical diverter 50 and the waveguide 42 b iscovered with reflective material 62 or 63 in the manner described abovewith respect to the waveguide 42 shown in FIGS. 2-4C. The top surface 56of the waveguide 42 b includes a depressed region or dimple 74 thatredirects light rays propagating in the waveguide 42 b, as describedbelow. As best shown in FIG. 22, the dimple 74 comprises a surface 75 ofsmooth and continuous curvature relative to the bottom surface 58 so asto define an area of reduced thickness of the waveguide 42 b. As usedherein, the “thickness” of the waveguide 42 refers to the distancebetween the top surface 56 and the bottom surface 58. In the preferredembodiment, the variation of thickness (e.g., depth of the dimple 74) isat least equal to 5% of the thickness of the waveguide 42 outside thedimple 74.

The dimple 74 is preferably centrally located with respect to theperiphery of the waveguide 42, covers an area at least 70% that of thetop surface 56, and defines an elliptical shape in a cross-sectionparallel to the top surface 56. For the rectangular waveguide, shown inFIG. 10, the geometric contour of the dimple 74 defines a super ellipsein accordance with the following equation:

(x/a)^(n)+(y/b)^(p)=1

where n and p are both greater than 2, a is the length of the major axisof the ellipse, and b is the length of the minor axis of the ellipse. Asis well known, increasing the exponents n and p above two causes theshape of the ellipse to become less oval and more rectangular. Theseexponents are preferably selected so that the curved edges of the dimple74 extend substantially to the edges of the output illumination regionof the waveguide.

According to an advantageous feature of the waveguide 42 b, the surface75 of the dimple 74 follows a geometric contour that redirects lightpropagating between the top surface 56 and the bottom surface 58, sothat the redirected light more readily and uniformly exits the topsurface 56 of the waveguide 42 b. Specifically, some light will beincident on the curved dimple surface 75 at an angle of incidence whichcauses it to refract through the top surface 56. Light having anincident angle within the critical range will be totally internallyreflected. Reflected light will be directed toward the bottom surface 58or side surface 28. The reflective material 62 adjacent these surfacesreflects the light toward the top surface 56 for transmissiontherethrough. Light reflected from the bottom surface 58 in the regionof the dimple 74 will typically be incident on the dimple surface7517-20 at a reduced angle of incidence which permits the light to betransmitted therethrough. Other embodiments may utilize multiple lightsources 44 with a single and multiple dimples 74.

As shown in FIGS. 12 and 13, another embodiment of the lightingapparatus, referred to as lighting apparatus 170, comprises arectangular waveguide 172 having a top surface 174 (FIG. 13) and anopposed bottom surface 176 (FIG. 13). Four side surfaces 178 a (FIG.13), 178 b (FIG. 13), 178 c, and 178 d extend between the top surface174 and bottom surface 176. A pair of lamps 180 a, 180 b are mountedadjacent the opposing side surfaces 178 a and 178 b. The lamps 180 a,180 b are preferably held in place by diffusive reflective material 182that surrounds the lamps 180 a, 180 b and covers a significant portionof the waveguide 172, as described more fully below.

The lamps 180 preferably comprise fluorescent tubes of circularcross-section which extend along substantially the entire length of thesides 178 a, 178 b. As best shown in FIG. 13, the sides 178 a and 178 bof the waveguide 172 are preferably each concave to form respectiveelongate channels that extend along the entire length of the sides 178a, 178 b. Such channels are configured to flushly receive respectivesurfaces on sides of the lamps 180 a, 180 b. An optical coupling gel 184is interposed between the lamps 180 a, 180 b and the sides 178 a, 178 bof the waveguide 172 in order to reduce repetitive index differences byeliminating air gaps therebetween and thereby efficiently couple lightfrom the lamps 180 a, 180 b to the waveguide 172. Alternatively, thelamps 180 a, 180 b may each comprise a linear array of point sources,such as LEDs (not shown).

In the preferred embodiment, the reflective material 182 entirely coversthe bottom surface 176 and wraps around the lamps 180 a, 180 b to secureand retain them in juxtaposition with the side surfaces 178 a, 178 b ofthe waveguide 172. The reflective material 182 also wraps around thesides 178 c, 178 d and extends onto a portion of the top surface 174 soas to form a peripheral strip 186 (FIG. 12) that extends around theperimeter of the top surface 174.

Accordingly, the interior surface of the reflective material creates anoptical cavity that is filled by the solid waveguide 172 and lamps 180.The portion of the top surface 174 of the waveguide 172 that is notcovered by reflective material 182 forms an illumination output regionor aperture 188 through which light is output from the waveguide 172.The peripheral strip 186 is sufficiently wide to shield the lamps 180from being viewed directly through the aperture 188. In the illustratedembodiment, the aperture 188 has a rectangular shape. It will beappreciated that the aperture 188 could also be circular or take on anyother of a wide variety of shapes suited for various applications.

An angular spectrum restrictor 190, such as described above inconnection with FIG. 9, may be juxtaposed with the aperture 188. In apreferred embodiment, the angular spectrum restrictor comprises abrightness enhancing film (BEF) 190, as described above, utilized with adiffuser 192 to collectively form a light quality enhancing (LQE)apparatus 196. A color filter 198 may be added to the LQE apparatus 196,if desired. In one embodiment, the edges of the LQE apparatus 196 areinterposed between the waveguide upper surface 174 and the peripheralstrip 186 of the reflective material 182 so that the reflective material182 secures the LQE apparatus 196 to the waveguide 172. Alternately, theLQE apparatus 196 may be positioned over the reflective material 182 andsecured using an adhesive.

The waveguide 172, lamps 180, reflective material 182, and LQE form alighting assembly that may be used as a downlight or a backlight. Thereflective material 182 reflects light from the lamps 180 a, 180 btowards the waveguide 172 so that substantially all of the light iscoupled into the waveguide 172 through sides 178 a, 178 b and theoptical gel 184. The light undergoes diffuse reflections within thewaveguide 172 before exiting from the waveguide 172 through the aperture188. In particular, the light reflects against the diffusive reflectivematerial 182 that covers the bottom surface 176, surrounds the sidesurfaces 178 a-178 d, and covers the peripheral strip 186.

In the lighting apparatus 170, pertinent design factors include the areaof the illumination aperture 188, and the combined cavity area, that isthe sum of (i) the surface area of the optical cavity and (ii) the areaof the aperture 188. For reasonably efficient use of the energy emittedfrom the lamps 180 a, 180 b the ratio of the area of the aperture 188 tothe combined cavity area is preferably at least 0.20, and in onepreferred embodiment the ratio is at least 0.40.

Another parameter of interest is the edge-to-edge dimension of theaperture 188, particularly the dimension referred to herein as thebisector dimension. This bisector dimension is an edge to edge dimensionthat extends between opposing sides of the aperture 188, along a linepassing through the geometric center of the aperture 188, andsubstantially perpendicular to the aperture edges at such opposing sides(or a tangent thereto in the case of a circular aperture). In oneembodiment, all of the edge-to-edge bisector dimensions of the outputregion are at least 4 inches in length. The ratio of the depth of thecavity to the edge to edge bisector dimensions affects both theintensity and uniformity of the light emanating from the opening formedby the aperture 188. In one preferred embodiment of the presentinvention, the ratio of the depth of the cavity to any of the edge toedge bisector dimensions is significantly less than 0.1, and preferablyno more than 0.08. In another embodiment, only the longest bisectordimension satisfies these ratios. In yet another embodiment, the ratiois no more than 0.03.

The waveguide 172 is comprised of material that is transparent to lightproduced by the lamps 180 a, 180 b, such as a transparent polymericmaterial, and may be manufactured by various well-known methods, such asmachining or injection molding. Preferred materials for the waveguide172 are acrylic, polycarbonate, and silicone.

As mentioned above in connection with the previous embodiments, thereflective material 182 has a reflectivity of at least 90% and maycomprise a single layer or multiple layers of diffusely reflective tape,such as DRP™ Backlight Reflector, manufactured by W. L. Gore &Associates. Alternately, the surfaces of the waveguide 172 may be coatedwith a reflective paint of the type described above.

The light emerging through the aperture 188 of the lighting apparatus170 may be used to illuminate a display or to provide illumination for aroom. In a preferred embodiment, the lighting apparatus 170 is used as aceiling light fixture. By way of example, when used as a light fixturefor a room, the waveguide 172 may be approximately 16″×4″ andapproximately 6 mm thick. The diameter of the lamps 180 preferably matchthe thickness of the waveguide 172.

Referring to FIG. 14, the lighting apparatus 170 may include a hollowhousing 200 comprising a planar upper portion 202, side portions 204a-204 d, and bottom portions 206 a and 206 b that together define ahollow space sized to receive the lighting assembly. The side portion204 a is pivotably mounted to one edge of the upper portion 202, therebyallowing it to be opened so that the lighting assembly may be slid intothe hollow space within the housing 200. Rails may be positioned on theside portions 204 b and 204 c to facilitate insertion of the lightingassembly into the housing 200.

As shown in FIG. 14, the bottom portions 206 a and 206 d define anopening 208 therebetween that is at least as large as the aperture 188.The lighting assembly is positioned within the housing 200 so that theillumination aperture 188 of the waveguide 172 is juxtaposed with theopening 208 in the housing 200. Power may be supplied to the lamps 180in any known manner, such as through an electrical ballast 210positioned in the housing 200 and connected to the lamps via electricalwires. When the lighting apparatus is illuminated, light emerges fromthe waveguide 172 through the aperture 188 and into the room.

FIGS. 15 and 16 illustrate yet another embodiment of a lightingapparatus utilizing a waveguide 42 c. As best shown in FIG. 15, the topsurface of the waveguide 42 includes a total internal reflection (TIR)region 76 having a smoothly curved surface 80 (FIGS. 16 and 16A)defining a vortex shape that extends into the waveguide 42. Preferably,the region 76 has the shape of an equiangular spiral that forms into acusp 82. Referring to FIGS. 16 and 16A, the surface 80 has a curvedshape that is symmetrical about a vertical axis 83 that extends throughthe cusp 82 and perpendicular to the top surface 56. A light source 44,preferably an LED, is mounted immediately below the cusp 82. The LED 44is embedded in a correspondingly-shaped hole, channel, or recess 84 thatextends into the bottom surface 58 of the waveguide 42 c. In order toensure good coupling into the waveguide 42 c and reduce reflections atthe interface between facets of the LED and corresponding sides of therecess 84, a transparent optical coupling agent, such as an adhesive orgel (not shown), may be used to fill any air gaps between the LED 44 andthe waveguide 42 a. The transparent optical coupling agent could be anepoxy, silicone, or any well-known organic or inorganic optical couplingmaterials. Preferably, the refractive index of the coupling agent isbetween that of the LED 44 and waveguide 42.

The surface 80 may be either a nonplanar, curved surface, or a nonplanarsurface comprising of a plurality of flat surfaces approximating a curvethat produces total internal reflection (TIR). As mentioned, the shapeof the surface 80 is preferably a symmetric section of an equiangularspiral. However, other geometric shapes can be used to produce totalinternal reflection including symmetric sections of hyperbolae,parabolas, sine curves and circles, provided that such shapes areanalytically shown to produce total internal reflection, as describedbelow. Mathematical modelling of these shapes can be performed with anoptical analysis software package such as ASAP by Breault Research ofTucson, Arizona. However, various parameters such as the waveguidethickness and the shape of the surface 80 must be optimized to optimizethe coupling of light into the waveguide 42 c.

The geometric contour of the surface 80 is selected so that the TIR cuspregion 76 formed thereby totally internally reflects substantially alllight rays directly emitted by the light source 44. Toward this end, thesurface 80 is contoured such that substantially all light rays emittedfrom the light source 44 are incident on the surface 80 at an angle atleast equal to the critical angle. This may be accomplished bycalculating the range of possible incidence angles of light rays fromthe light source 44 at various local areas of the surface 86. The localareas are then oriented so that all rays are incident within thecritical range. The local areas could be large in size so that thesurface 80 consists of a collection of flat surfaces. As the size of thelocal areas decreases, the surface 80 forms into a smoothly curvedsurface having an equiangular spiral shape as shown in FIGS. 16 and 16A.

In the embodiment illustrated, the bottom surface 58, side surfaces 60,and the back of the LED are covered by the diffusive reflective material62. When the light source 44 is energized, the light totally internallyreflected from the surface 30 propagates within the waveguide 42 outsideof the TIR cusp region 76. The reflective material 62 functions in themanner described with reference to the waveguide 42. This embodiment isparticularly advantageous when the waveguide is utilized as a tail lightlens for an automobile. It is contemplated that multiple TIR cuspregions 76 could be positioned on a waveguide 42C, and thus the totalcombined area of illumination may be quite large.

FIGS. 17 and 18 illustrate an alternative embodiment of the TIR cuspregion 76 used in a waveguide 42 d. Referring to FIG. 17, the TIR region76 is elongated so as to define an elongated cusp 82 a that extendsalong an axis 83. The TIR region 76 comprises top and bottom equiangularspiral curved surfaces 86, 88 (FIG. 18) that symmetrically extend fromeither side of the elongated cusp 82 a. In the illustrated embodiment, aTIR region 76 is located on both the top surface 56 and the bottomsurface 58, although the TIR region could also be located on a singlesurface.

A light source 86 is mounted immediately below the elongated cusp 82.The light source 86 may consist of a single elongated light source thatextends along the entire length of the cusp 82, such as a fluorescenttube. Alternatively, the light source 86 may consist of a plurality ofpoint light sources, such as LEDs, that form a line aligned immediatelybelow the length of the cusp 82. The tip of the elongated cusp 82 may berounded to provide controlled leakage of light from the light source 86in the area of the waveguide 42 d immediately above the light source 86.This will eliminate dark spots above the light source 86.

The waveguide 42 d shown in FIGS. 17 and 18 functions in essentially thesame manner as the waveguide shown in FIGS. 12-13. That is, the TIRregion 76 totally internally reflects substantially all light emitted bythe light source 86. The symmetric pair of curved surfaces 86, 88 joinedat the elongated cusp 82 a provide total internal reflection (TIR) ofthe light from the light source 44 along either side of the axis 83. Thecusp 82 a divides the light from the light source 44 into two equalportions.

Because the TIR cusp regions 76 of FIGS. 15-18 reflect substantially alllight incident thereon, these regions 76 will appear dark relative toportions of the waveguide outside the TIR regions 76. In situationswhere such dark spots are objectionable, the surface 80 should becontoured to be a less than perfect internal reflector so that asignificant portion of the incident light leaks through the surface 80.The amount of leakage should preferably be no more than is necessary tosubstantially eliminate the dark spots, and provide an intensity in theTIR regions substantially equal to that of the surrounding region. Suchleaky TIR regions thus provide substantially uniform output illuminationacross the entire output region of the waveguide.

LEDs have many desirable properties for optical display systems,including low cost and low driving voltage. LEDs are capable ofproducing various colors, such as red, green and blue. The drivingvoltage of an LED may vary from 1.8 volts to 4.0 volts, and thedifferential energy levels of the quantum mechanical bandgap producesthese spectral colors. However, those skilled in the art will appreciatethat other point sources may be used. Laser diodes (Lds) orsuperluminescent light emitting diodes could be used, as well as anysemiconductor light emitting device.

FIG. 19 shows a conventional prior art LED 110 in a “bullet lens”package. The LED 110 includes a housing 111 that encloses two electricalleads 112 connected to an anode 113 and a cathode 114. A layer 115 ofGroup HI-V semiconductor compound, such as A1GaAs, GaAsP, or A1InGaP, isinterposed between the anode 113 and cathode 114. A cup-shaped reflector116 is positioned behind the semiconductor layer 115. The top portion ofthe housing 111 forms a hemispherical immersion lens 117 made of anacrylic or an epoxy.

When a voltage in the range of 1.8-4.0 V is applied between the anode113 and cathode 114, the LED produces visible light energy according tothe photoelectric effect. The reflector 116 reflects the light in anupward direction so that the light does not pass through the sides ofthe housing 111. The lens 117 focuses the light emitted by thesemiconductor layer 115. The semiconductor material has a refractiveindex of approximately 3.4 and the index of refraction of the plasticpackage of the housing 6 is 1.5.

FIG. 20 shows a conventional prior art “bare” light emitting diode 110a. The LED 110 a includes a semiconductor layer 115 a positioned on aflat base 117. A dielectric dome 118 covers the semiconductor layer 115.A reflector 116 a is positioned between the base 117 and thesemiconductor layer 115.

FIG. 21 shows an exit sign 130 illuminated in accordance with anotherembodiment of the invention. The exit sign 130 consists of a planarwaveguiding layer or waveguide 132 having a surface 134 on which anillumination coupling element 136 is centrally located. The illuminationcoupling element 136 produces and couples illumination from LEDs 140into the waveguide 132. A plurality of display elements 142 are alsolocated on the surface 134 for coupling the light from the waveguide 132to an external viewer 144.

Referring to FIG. 21, the display elements 142 have shapes that form theletters “E”, “X”, “I”, and “T”, although the display elements may formany of a wide variety of symbols and shapes for illumination. Forinstance, for illuminating a tail light (FIG. 22), the display elements142 might be in the form of elongate structures, such as horizontal orvertical lines or channels in the tail light surface. In an alternativeembodiment for illuminating a watch or clock face (FIG. 23), the displayelements 142 might be in the form of numbers or dots on the dial. For awatch using display elements 142, a single LED could be located in theinterior region of a circular waveguide on the watch face.Alternatively, four LEDs could be located in the interior of the watchface, with each LED illuminating one quadrant of the watch face, such asshown in FIG. 23. Additionally, the LEDs could be arranged in a circulararray with equiangular spacing.

FIG. 24 illustrates a cross-sectional view of the waveguide 132. Asshown, the display elements 142 are concave structures that extend intothe surface 134. The display elements 142 could also be convexstructures. The surfaces of the display elements 142 may either besmooth surfaces or rough surfaces to increase optical diffusion.

As shown in FIG. 24, the illumination coupling element 136 includes oneor more LEDs 140 that are embedded in a bottom surface 146 of thewaveguide 132. The LEDs 20 are preferably oriented with theirlongitudinal axes normal to the bottom surface 146 of the waveguide 132.The LEDs 140 may be embedded in either surface 142 or 146 of thewaveguide 132, but are preferably embedded in surface opposite locationof the display elements 142. The LEDs 140 could consist of either“bullet lens” LEDs or “bare” LEDs.

As shown in FIG. 24, the illumination coupling element 136 comprises aTIR region 150 having curvilinear surfaces 152, 154 similar to surfaces86 and 88 described above with respect to FIGS. 14 and 15. The surfaces86 and 88 curve toward the LED 140 to receive impingement of light fromthe LED 140. The surfaces 86 and 88 are TIR surfaces with respect tosuch impingement of light. As shown, the surfaces 86, 88 form a cuspdirected toward the LED 140 with the LED 140 having an end terminatingin alignment with the cusp to direct substantially all light from theLED directly toward and adjacent the cusp. The TIR region operates insubstantially the same manner described above and therefore no furtherdescription is provided.

The illumination coupling element 136 desirably includes a lens element90 that is integrally formed with the surface of the waveguide that isadjacent to the LED 140. The optical power of the lens element 90 iscaused by a refractive index differential between an air gap surroundingthe LED 140, the LED 140, the transparent optical coupling agent, andthe waveguide 132. In this embodiment of the waveguide 132, thetransparent optical coupling agent and the material of the LED 140preferably all have an index of refraction of about 1.5. An air gaparound the LED 140 defines a volume with a refractive index of about 1.0to cause refraction of light.

The lens element 90 may optionally be either convex or concave. A convexlens element 90 converges light from the LED 140 to reduce the angularextent of the light radiation from the LED 140. In one embodiment, thefocal power of convex lens element 90 is sufficient to collimate thelight rays. A concave lens element 90 diverges light rays emanating fromthe LED 140 to increase the angle of the light rays on the surfaces 152and 154. This increases the likelihood of light rays intersecting thesurfaces 152 and 154 at an angle of incidence greater than the criticalangle.

FIG. 25 illustrates another embodiment of an exit sign 130 generallycomprising a waveguide 132 a. In this embodiment, LEDs 140 arepositioned facing outwardly within a circular coupling element 148located in an interior light injection region of the waveguide 132 a.The longitudinal axes of the LEDs 140 are desirably oriented parallel tothe plane of the surface 134. Although FIG. 25 shows four LEDs 140separated by 90° angles in the coupling element 148, it will beappreciated that any number of LEDs 140 can be arranged around theperimeter of the coupling element 148. The LEDs 140 may also be arrangedin shapes other than circles, with the longitudinal axes preferablyaligned parallel to the waveguide 132 a, such as, for example, ovoid,rectangular, square, and linear shapes.

The coupling element 148 may either be integrally formed with thewaveguide 132 a or it may be modularly inserted into a correspondinghole or recess in the waveguide 132 a so that light is injected throughthe sides of the hole and perpendicular thereto. For a modularconfiguration, LEDs 140 are desirably first mounted onto the couplingelement 148 and then the coupling element 148 is inserted into the holeor recess in the waveguide. A modular insertion technique providesadvantages in manufacturing by making it easier to manipulate aplurality of light emitting diodes (LEDs) simultaneously. If thecoupling element 148 is integrally formed in the waveguide 132 a, theLEDs 140 are inserted directly into the hole or recess in the waveguide.In one possible application ‘bare’ LEDs may be grown directly on thesurface of the waveguide.

In another embodiment shown in FIG. 26, extractive display elements 300are used in combination with a sign 130 comprising a waveguide 132 c. Anillumination coupling element 136 is used to inject light into thewaveguide 132 in the manner described above. A plurality of extractivedisplay element 300 and waveguiding cylinders 302 are patterned into thesurface of the waveguide 132 c, as described below. The extractivedisplay elements 300 appear as a series of pointed bumps that arearranged in the shape of symbolic or nonsymbolic figures. Uponillumination through the waveguide 132 c and the waveguiding cylinders302, and in combination with illumination couplers, such as a TIR regiondescribed above, the extractive display elements 300 produce aparticularly bright, point-like (or line-like) light pattern at theapexes (or vertexes) of the solid polygons.

FIG. 27 shows a side view of an extractive display element 300 formed onthe end of a waveguiding cylinder 302. The base of the extractivedisplay element 300 is integral with the end of the waveguiding cylinder302. Preferably, each of the waveguiding cylinders 302 has a diameter onthe order of one-tenth of one inch (0.1″), although the diameter of acylinder may be as small as on the order of one-thousandth of an inch(0.001″).

In the embodiment shown in FIG. 27, the extractive display element 300is in the shape of a polygonal solid having three equilateral faces 304,306, 308, and an apex 310 with 120 degree vertices. The number of faceson the extractive display element 300 is not limited to three, and couldbe any number from two or more. A two-sided extractive display element300 would be a wedge shape at the end of the cylinder, appearing muchlike the tip of a screwdriver. A greater number of faces on theextractive display element 300 could include rectangular, hexagonal,octagonal, and circular shapes. In the case of a circular extractivedisplay element 300, the cylinder preferably tapers to a conical tip.Any other wide variety of shapes, such as cross or star shapes, are alsocontemplated.

The shape of the extractive display element 300 produces a particularlybright, point-like (or line-like) light output at the apex (or vertex)310. Light is transmitted by total internal reflection within thewaveguiding cylinder 302 until it enters the waveguide cylinder 302 andextractive display element 300 through lateral portion 312. Light withinthe extractive display element 300 is confined within the equilateralfaces 304, 306, 308 by total internal reflection until it comes withinthe vicinity of apex 310. Light is then efficiently coupled out of thedisplay element 300 as a bright, point-like (or line-like) output byapex (or vertex) 310.

As shown in FIG. 29, the length of the waveguiding cylinder 302 may bereduced so that the display element 142 consists of only the extractivedisplay element 300 formed directly on the surface 134. These extractivedisplay elements 300 are further disclosed in co-pending patentapplication Ser. No. 08/683,757, entitled “Light Extractor Apparatus,”assigned to the same assignee. It has been found that these extractionelements efficiently extracting excess of 90% of incident radiation withless than 10% backscatter.

The base of each waveguiding cylinder 302 is preferably formed integralwith the surface of the waveguide 301 to facilitate ease ofmanufacturing. The extractive display elements 300 and waveguidingcylinders 302 may be formed by conventional methods of molding plasticarticles, such as injection or compression molding.

The contrast of the sign 130 utilizing extracting display elements 300may be equalized by varying the characteristics of the display elements300 across the surface of sign 130. For example, the diameters of thecylinders 302 that are closer to the illumination coupling means may bemade less than the diameters of the cylinders 302 that are farther awayfrom illumination coupling means to compensate for the greater lightintensity that is typically present in the central regions of the sign.Decreasing the diameter of the cylinder 302 reduces the quantity oflight that is delivered to the apex (or vertex) of the extractivedisplay element 300.

FIG. 29 shows an exit sign 130 comprising a waveguide 132 d. Anillumination coupling means 318 is positioned in the interior of thewaveguide 132 d for injecting light into the waveguide 132 d. Theillumination coupling means include a plurality of LEDs 140. Thewaveguide 132 d includes a series of concentric grooves 320 located on aback surface of the waveguide 132. The concentric circular grooves 320preferably radiate outward from the central region of the waveguide 132d. The circular grooves 320 are positioned only in the areas where thesymbolic or nonsymbolic characters of the sign are to be displayed andilluminated so that the circular grooves 320 form the shape of thecharacters. Preferably, utilizing concentric circular grooves 320further optimizes the display by matching the symmetry of the lightsource or obtaining other desirable display properties.

As shown in FIG. 30, the concentric circular grooves 320 are V-shapedstructures that act to reflect light through the opposite side of thewaveguide 132 d. The grooves 320 define an angle between the surfaces ofthe “V,” although the grooves may take other shapes than “V's”. Thecircular grooves 320 differ from the display elements 142 both in thesize and location. The depth of the circular grooves 320 may be only onthe order of one-tenth of one percent (0.1%) to one percent (1%) of thewaveguide 132 d thickness.

The grooves 320 may be formed by any of a variety of methods includingmachining (mechanical, laser, or EDM), ablation, etching, stamping orembossing. They can also be formed initially over the entire surface ofthe waveguide and then subsequently filled in with an index matchingmaterial in all of the areas except those corresponding to thecharacters of the display. A decal film or screen may be applied to formthe characters or to subsequently remove all but the selected areas. Itis also possible to optimize the display characteristics by changing theproperties of the grooves 320 at different points on the display. Thespatial frequency, width or depth of the grooves 320 may increase atregions further removed from the illumination coupling means 318 inorder to obtain desirable display characteristics.

Although the foregoing description of the preferred embodiments haveshown, described, and pointed out certain novel features of theinvention, it will be understood that various omissions, substitutions,and changes in the form of the detail of the apparatus as illustrated aswell as the uses thereof, may be made by those skilled in the artwithout departing from the spirit of the present invention.Consequently, the scope of the present invention should not be limitedby the foregoing discussion, which is intended to illustrate rather thanlimit the scope of the invention.

What is claimed is:
 1. An illumination device, comprising: a waveguidehaving an illumination coupler embedded in an interior region of saidwaveguide, said illumination coupler adapted to receive light from apoint source within said interior region, and to direct light betweengenerally parallel top and bottom surfaces outside said interior region,said illumination coupler comprising a refractive index interface whichis inclined relative to at least one of said top and bottom surfacessaid interface being configured to reflect light rays emitted by thepoint source which propagate along a line that forms less than thecritical angle of total internal reflection with respect to a line lyingin one of said top and bottom surfaces, such that light rays which wouldotherwise pass out of said waveguide are captured for propagationbetween said top and bottom surfaces.
 2. The illumination device ofclaim 1, wherein said illumination coupler comprises a surfaceconfigured for total internal reflection of light incident thereon. 3.The illumination device of claim 2, comprising a point source of lightdisposed at least partially within a cavity in said waveguide, saidcavity being adjacent to said total internal reflecting surface.
 4. Theillumination device of claim 3, comprising display elements on one ofsaid top and bottom surfaces for ejecting light from said waveguide. 5.The illumination device of claim 3, comprising diffusive reflectivematerial on one of said top and bottom surfaces.
 6. The illuminationdevice of claim 1, wherein the waveguide and illumination coupler areintegrally formed from a single piece of material.
 7. An illuminationdevice comprising, in combination, a) a waveguide for light, anddefining a substantially flat light travel channel, b) an LED closelyassociated with the waveguide, c) and there being a surface on thewaveguide curving toward the LED to receive impingement of light fromthe LED, said surface being a TIR surface with respect to saidimpingement of light from the LED, for re-directing such light to travelalong said light travel channel, said surface defining a cusp directedtoward the LED, said LED having an end terminating in alignment withsaid cusp to direct substantially all light from the LED directly towardand adjacent the cusp.
 8. The device of claim 7 wherein said LED has alight-emitting portion located within a boundary defined by saidwaveguide.
 9. The device of claim 7 wherein said waveguide has a bodyand said surface is concave adjacent the waveguide body.
 10. The deviceof claim 7 wherein said surface is concave toward said channel.
 11. Thedevice of claim 7 wherein said surface defines an axis directed towardthe LED.
 12. The device of claim 11 wherein said surface defines an axisthat intersects said cusp and said LED.
 13. The device, as defined inclaim 7, and comprising: said waveguide is an optical waveguiding layer;and including display elements formed on said waveguiding layer to causelight to be emitted from said waveguiding layer.
 14. The device of claim13, wherein: said display elements are formed as concave channels withinthe surface of the waveguiding layer, and external surfaces of saidchannels are either smooth or rough to promote diffuse output radiation.15. The device of claim 14, wherein: said concave channels of saiddisplay elements have depths across said waveguiding layer thatcompensate for differences in said illumination.
 16. The device of claim15, wherein: said concave channels of said display elements are deepertowards outer portions on said waveguiding layer of said display devicethan are said concave channels towards central portions of saidwaveguiding layer of said display device.
 17. The device of claim 13,wherein: each of said display elements is a polygon solid having an apexor a vertex on a line normal to said waveguiding layer.
 18. The deviceof claim 13, wherein: each of said display elements has the form of apolygon solid having two or more equilateral side faces.
 19. The deviceof claim 13, including: a lens element incorporated integrally to thesurface of said waveguiding layer.
 20. The device of claim 13, wherein:said waveguiding layer has an overall shape that is thin relative to itslength.
 21. The device of claim 13, wherein: said display elements arearranged in alphanumeric patterns.
 22. The device of claim 13, wherein:said LED is a bullet lens package light emitting diode.
 23. The deviceof claim 13, wherein: there is an air gap formed between said LED andsaid waveguiding layer.
 24. The device of claim 13, wherein: said LED isembedded in said waveguiding layer by optically coupling said LED tosaid waveguiding layer with an optical coupling agent.
 25. The device ofclaim 24, wherein: said optical coupling agent is one of the following:a silicone adhesive, gel, grease, an epoxy polymer.
 26. The device ofclaim 13, wherein: said display elements are concentric circular groovesin a surface of the waveguiding layer, said concentric circular groovesbeing present only in areas corresponding to symbolic or nonsymboliccharacters.
 27. The device of claim 7, wherein: said display elementsare retroreflective corner cube elements.
 28. An optical apparatus,comprising: an LED; an optical element having generally parallel top andbottom opposing sides and an edge extending between the top and bottomopposing sides, said LED mounted at a predetermined location adjacent acentral portion of one of said opposing sides such that light from theLED enters the optical element, said optical element including a TIRsurface spaced from said one opposing side and extending from a pointadjacent the predetermined location of the LED outwardly towards saidedges such that said light entering the optical element is directedagainst said TIR surface, said TIR surface curving in the vicinity ofthe LED so as to form a cusp adjacent the LED, the curving TIR surfacehaving a curvature which totally internally reflects light rays incidenton said TIR surface and redirects such light rays through said opticalelement, whereby such light rays do not pass through the other opposingsurface.
 29. The apparatus of claim 28, wherein the cusp is in the formof an equiangular spiral.
 30. An optical apparatus, comprising: a lightemitting diode (LED); an optical element having top and bottom opposingsides and an edge extending between the top and bottom opposing sides,said LED mounted at a predetermined location beneath a central portionof said optical element such that light from the LED enters the opticalelement, said optical element including a TIR surface spaced from saidbottom side and extending from a point above the LED outwardly towardssaid edges, said TIR surface positioned to receive light emitted by theLED, said TIR surface curving towards the LED so as to form a cusp abovethe LED, the curving TIR surface totally internally reflecting lightrays such that reflected light rays propagate from the TIR surfacetowards the edge of the optical element.
 31. The optical apparatus ofclaim 30, wherein said TIR surface is circularly symmetric.
 32. Theoptical apparatus of claim 31, wherein said TIR surface has avortex-like shape.
 33. The optical apparatus of claim 30, wherein saidTIR surface is leaky such that some light emitted by the LED istransmitted therethrough.
 34. The optical apparatus of claim 33, whereinsaid cusp is contoured to permit leakage of light through said TIRsurface.
 35. The optical apparatus of claim 34, wherein said cusp isrounded to permit leakage of light through said TIR surface.
 36. Theoptical apparatus of claim 30, wherein said optical element comprisespolymeric material.
 37. The optical apparatus of claim 36, wherein saidoptical element comprises material selected from the group comprisingacrylic, polycarbonate, and silicone.
 38. An optical apparatus,comprising: a light emitting diode (LED); an optical element positionedto receive light from the light emitting diode, said element comprisedof a refractive index interface having a curved shape that issymmetrical about an axis and converges to a location in a centralportion of the optical element, said location and said light emittingdiode lying substantially on said axis, said interface being shaped andpositioned relative to said LED to reflect a substantial portion oflight from said LED in a direction transverse to said axis.
 39. Theoptical apparatus of claim 38, wherein said refractive index interfaceis circularly symmetric.
 40. The optical apparatus of claim 39, whereinsaid curved shape conforms to the shape of a vortex.
 41. The opticalapparatus of claim 38, wherein said refractive interface surfaceconverges to form a cusp which terminates at said location.
 42. Theoptical apparatus of claim 41, wherein said cusp is contoured to permitleakage of light through said central portion of said refractive indexinterface.
 43. The optical apparatus of claim 42, wherein said cusp isrounded to permit leakage of light through said central portion of saidrefractive index interface.
 44. The optical apparatus of claim 38,wherein said refractive index interface has a shape of an equiangularspiral.
 45. The optical apparatus of claim 38, wherein said refractiveindex interface is leaky such that some light emitted by the lightemitting diodes transmitted therethrough.
 46. The optical apparatus ofclaim 38, wherein said optical element comprises polymeric material. 47.The optical apparatus of claim 46, wherein said optical elementcomprises material selected from the group comprising acrylic,polycarbonate, and silicone.
 48. The optical apparatus of claim 46,wherein said refractive index interface comprises an air/polymerinterface.